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Avalanche Forecast

Archived

Apr 2nd, 2017–Apr 3rd, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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Use caution in steep terrain especially if the surface snow is wet more than a few inches, avoiding steep slopes above terrain hazards such as trees or cliffs. Avoid travel on or below cornices.

Detailed Forecast

Showers should remain light at higher elevations along the Cascade east slopes on Sunday with cooler temperatures.

This should not greatly change the regional avalanche danger on Sunday.

Expect shallow loose wet snow conditions over one or more strong near surface crust layers mainly on solar slopes.

Recent cornices are very large. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.

Recent large wind slabs should have mostly stabilized where formed on lee slopes, mainly above treeline and on NW-SE aspects, but will remain listed as an avalanche problem in the Northeast zone for higher terrain that received storm snow Wednesday.

Snowpack Discussion

Special Note: For more information on the massive natural cornice triggered avalanche on the north side of Ruby Mountain on Sunday 3/19 and general thoughts about low-likelihood/high consequence avalanches, please see NWAC's blog post issued Sunday, March 26. 

Weather and Snowpack

Let's just say it's been a wet and wild few weeks regarding weather and avalanches in the Cascades. 

Last week was also active weather-wise, but water amounts/snowfall totals were slightly lower relative to the extreme wetness of the past few weeks. NWAC and NRCS stations east of the Cascade crest had about 6-12 inches of snow in the 5 days ending Monday morning.

A strong low pressure system brought rising snow levels and locally heavy precipitation Tuesday night through Wednesday. Another 5-10 inches fell near the Cascade crest along with a warming trend and increasing W-SW alpine winds Tuesday night and into Wednesday. Lesser amounts were seen further east of the crest and at lower elevations. 

Cooling and showery weather Thursday allowed wet snow to begin refreezing with light amounts of new snow in most areas. The winds diminished by Thursday and combined with daytime warming, this has allowed for wind slab and storm slab to begin stabilizing.

Very mild temperatures and increased solar radiation Friday allowed for wet surface snow conditions in most terrain, even northerly facing slopes.

A weak front crossed the Northwest on Saturday morning causing light rain mainly along the Cascade west slopes.

Recent Observations

North

The NCMG were in the Cutthroat area on Monday and found 15-20 cm of recent snow on a firm base. Loose wet avalanches and cornices were the main concerns. 

On Tuesday, the NCMG in the Highway 20 Hairpin area found that ski and hand tests indicated good bonds of recent snow to previous snow. Loose wet avalanches were the main concern at lower elevations. Touchy or stubborn wind and storm slab, and cornices were still expected near and above treeline.

A public observation from the Washington Pass area on Tuesday reported small ski triggered 10 in wind or storm slab on steep E slopes near a ridge line.

Central

No recent observations. 

South

No recent observations. 

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.